Conventional air conditioners are known that are capable of switchable cooling and heating operation or simultaneous cooling and heating operation, and include a plurality of utilization units, and a heat source unit. Each utilization unit includes a utilization side refrigerant circuit that includes a utilization side heat exchanger and a utilization side expanding means. The heat source unit includes a heat source side refrigerant circuit that includes a compressing means that compresses a refrigerant, a main heat exchanger, a first switching means for making the main heat exchanger to function as an evaporator and a condenser, and a main refrigerant switching means that includes a motor operated expansion valve capable of regulating the refrigerant flow of the main heat exchanger. The utilization side refrigerant circuit and the heat source side refrigerant circuit are connected via a connecting refrigerant circuit. In such an air conditioner, the load of the heat source unit is regulated according to the load of the plurality of utilization units, and operation is performed so that the thermal balance of the entire refrigeration cycle is satisfied. For example, the air conditioner is constituted so that the main heat exchanger is actuated as the evaporator during heating operation or during simultaneous cooling and heating operation; therefore, the amount of evaporation of the refrigerant is varied in the main heat exchanger by regulating the opening of the main refrigerant switching means, thus balancing the load of the utilization units and the load of the heat source unit. At this time, the variation in the amount of evaporation of the main heat exchanger is achieved by regulating the opening of the main refrigerant switching means while fixedly maintaining the high pressure refrigerant pressure on the discharge side of the compressing means of the heat source unit. In other words, if the amount of evaporation of the refrigerant in the main heat exchanger is greater than the amount of evaporation of the refrigerant corresponding to the load of the utilization units, then the amount of evaporation of the refrigerant is reduced by restricting the opening of the main refrigerant switching means because there is a tendency for the high pressure refrigerant pressure on the discharge side of the compressing means of the heat source unit to increase. Conversely, if the amount of evaporation of the refrigerant in the main heat exchanger is less than the amount of evaporation of the refrigerant corresponding to the load of the utilization units, then the amount of evaporation of the refrigerant is increased by enlarging the opening of the main refrigerant switching means because there is a tendency for the high pressure refrigerant pressure on the discharge side of the compressing means of the heat source unit to decrease.
As an example of another conventional air conditioner, one is known that provides, inside the heat source unit, an auxiliary heat exchanger provided in parallel with the main heat exchanger and that functions as the condenser. This air conditioner is constituted so that the load of the utilization units and the load of the heat source unit are balanced by regulating the thermal balance of the entire heat source unit by actuating and stopping the auxiliary heat exchanger. In other words, if the amount of evaporation of the refrigerant in the main heat exchanger is greater than the amount of evaporation of the refrigerant corresponding to the load of the utilization units, then there is a tendency for the high pressure refrigerant pressure on the discharge side of the compressing means of the heat source unit to increase; consequently, the thermal balance of the entire heat source unit is regulated by actuating the auxiliary heat exchanger to increase the amount of condensation and to offset the amount of evaporation of the refrigerant of the main heat exchanger. Conversely, if the amount of evaporation of the refrigerant in the main heat exchanger is less than the amount of evaporation of the refrigerant corresponding to the load of the utilization units, then there is a tendency for the high pressure refrigerant pressure on the discharge side of the compressing means of the heat source unit to decrease; consequently, the thermal balance of the entire heat source unit is regulated by stopping the auxiliary heat exchanger to decrease the amount of condensation.
An air conditioner is also known that includes both the above mentioned main refrigerant switching means and the auxiliary heat exchanger. Such an air conditioner is basically constituted so that the loads of the utilization units are balanced by actuating and stopping the auxiliary heat exchanger to regulate the thermal balance of the entire heat source unit, and so that fine adjustment is performed by regulating the opening of the main refrigerant switching means.
In an air conditioner that balances the load of the utilization units and the load of the heat source unit by regulating the thermal balance via the main refrigerant switching means and the auxiliary heat exchanger of the heat source unit, the greater the condensing capacity of the auxiliary heat exchanger is with respect to the evaporative capacity of the main heat exchanger, the more the range of regulation of the heat source unit with respect to the fluctuation in the load of the utilization units is unfortunately limited. For example, if the capacity of the auxiliary heat exchanger is increased, then the fluctuations in the refrigerant pressure on the high pressure side may unfortunately increase due to actuating and stopping of the auxiliary heat exchanger. Conversely, if the capacity of the auxiliary heat exchanger is decreased, then the range over which regulation must be performed by the main refrigerant switching means unfortunately increases; consequently, it may no longer be possible to restrict the amount of evaporation of the main heat exchanger particularly if the heating load of the utilization units is small.
Thus, in a conventional air conditioner capable of switchable operation or simultaneous cooling and heating operation, it is problematic to optimize the thermal balance of the heating load of the utilization units and the evaporative performance of the heat source unit while maintaining controllability.
In addition, in the above mentioned conventional air conditioner for switchable cooling and heating operation and the air conditioner for simultaneous cooling and heating operation, the model of the utilization units is shared, but the model of the heat source unit varies, which leads to an increase in manufacturing costs.